1. Field of the Invention
The present invention relates to a method of planning paths for mobile robots, such as autonomous carrier vehicles, and, more particularly, to a method of planning curved paths for mobile robots.
2. Description of the Prior Art
Unmanned carrier vehicles are classified into those of a guide line system which runs along paths defined by magnetic tapes or guide lines and correct positional error from the paths by a guide sensor attached to the bottom of the body, and those of autonomous system called autonomous vehicles. The autonomous vehicle is provided, for example, with a command system and a location system. The command system gives the location system commands at a given time interval through communication means to specify running paths. The command system of such an autonomous vehicle divides paths into segments, divides each into a number of points, determines a reference posture at each point, and controls the autonomous vehicle by feedback control with reference to a desired speed and an angular speed produced on the basis of the coordinates of the points and reference postures of the autonomous vehicle at the points.
Conventional path planning methods for such an autonomous vehicle system define a curved segment, in most cases, by a circular arc or a combination of circular arcs. However, since the curvatures of a circular arc at any point including its opposite ends are not zero, the curvature changes discontinuously at a junction of two circular arcs or a junction of a circular arc and a straight segment, even if the two circular arcs, or the circular arc and the straight segment are joined with tangent direction continuity.
Accordingly, although no problem arises in causing a conventional autonomous vehicle to travel along straight paths, it is liable to occur that the autonomous vehicle deviates from a correct path to overshoot at a junction of two path segments, because it is impossible to make the autonomous vehicle follow instantaneous, and discontinuous variations of curvature.